1. Field of the Invention
The present invention relates to a saddle-riding vehicle.
2. Description of the Related Art
Some motorcycles have a structure in which a fuel tank is disposed under a flat footboard due to reasons such as increasing the capacity of a storage box (see, e.g., Japan Laid-open Patent Application Publication No. JP-A-2007-8316).
On the other hand, saddle-riding vehicles have been demanded to dispose a catalyst to process exhaust gas as upstream as possible within an exhaust pipe in order to quickly activate the catalyst. For example, Japan Laid-open Patent Application Publication No. JP-A-2013-36422 discloses a motorcycle including a catalyst disposed upstream of a silencer.
Further, the motorcycles described in JP-A-2007-8316 and JP-A-2013-36422, respectively include an engine unit composed of an engine, an exhaust pipe connected to the engine, and a silencer connected to the exhaust pipe. The engine unit is of a so-called unit swing type and is pivotably supported by a vehicle body frame. The engine unit is disposed under a seat. A flat footboard, on which a rider puts his/her feet, is disposed under and forward of the seat. The flat footboard is disposed forward of the engine unit. A required space is reliably provided when the flat footboard is disposed under and forward of the seat due to the structure that the engine unit is disposed under the seat and is pivotably supported by the vehicle body frame.
The temperature of the catalyst becomes higher than that of the exhaust pipe. Further, in one type of saddle-riding vehicle in which the engine is at least partially disposed under the seat, the farther the catalyst is disposed upstream, the closer the catalyst is to the foot of the rider. Hence, it is required to consider the thermal effect of the catalyst on the foot of the rider.
On the other hand, in another type of saddle-riding vehicle including the flat footboard, the engine is disposed rearward of the flat footboard. Thus, when the fuel tank is disposed under the flat footboard, the farther the catalyst is disposed upstream, the closer the catalyst is to the fuel tank. Hence, it is also required to consider the thermal effect of the catalyst on the fuel tank.
Further, in terms of, for instance, a rider's easiness in getting on and off the vehicle, a footrest portion of the flat footboard is preferably wide in the width direction of the vehicle and is also preferably disposed in a low position. When the fuel tank is disposed under the flat footboard, the fuel tank is required to be wide in the vehicle width direction so as to have a large capacity. Thus, when the catalyst is located upstream, the fuel tank is likely to be affected by the catalyst.